Some Aspects Of The Biology And Population Dynamics Of Goatfish, Upeneus Spp. In Terengganu Waters, Peninsular Malaysia

Abstract

Two species of goatfish or Biji nangka, Upeneus
sulphureus and U . bensasi play a significant role in the
demersal trawl fishery in the Terengganu waters. Estimation
of their population parameters, i.e., growth, reproductive
behaviour, mortality rate, and assessment of the effect of
changes in exploitation pattern were carried out, and
alternative management measures for the fishery were
examined.Growth parameters were estimated based on modal
progression analysis of length frequency distributions.
Data on sexual maturity and seasonal changes in the
gonadosomatic index were used to elucidate the reproductive
biology of the two species .Length-based catch curves were
used to estimate total mortality rate ( Z ) while empirical
and indirect methods were used to estimate natural mortality rate (M). Relative yield per recruit as a
function of exploitation rate E , ( E= F / ( F+M) , ratio of
natural mortality M and Von Bertalanffy growth parameter
K , ( M/ K ) , and size at first capture (Lc ) , was used to
analyze the effects of variability in the controlled
variables E and/or Lc.Estimates of the growth parameters derived from eight
different methods were K = 0.80 to 1 .4 5 , Loo = 218.08 to
232.00 mm for U. sulphureus and K = 0.90 to 1.38 , Loo
22 8.00 to 243 .31 mm for U. bensasi. Estimates of total
mortality derived from three different methods employed
varied ( Z = 3.30 to 5.93 for U. sulphureus and Z = 2 . 65
to 5.57 for U . bensasi) so considerably that the validity
of the methods was questioned. Further validation of the
results derived from the length-based method is necessary. Estimates of natural mortality derived from three different
methods for upeneus sulphureus (M = 1.01 to 2 .53 ) were less
varied than for Upeneus bensasi (M = 1 .18 to 2.84 ). Finally , consideration of management policy using an
EO .1 criterion ( analogous to F0.I ) showed that the current
level of exploitation rate ( E =0.63 ) for U. sulphureus
exceeded the estimate of the E 0. I level ( E =0.5 7 ) , while
for U. bensasi ( E=0 . 51) it was below the E0.1 level
( E=0.6 7 ).